Articles are labeled to identify the contents of containers and provide attractive point of sale product presentation. Labels are applied by roll-fed, sleeve, or cut and stack methods. Different labeling materials have been developed including paper labels, film labels, laminated film and paper labels, styrene foam, and laminated film and foam. The appearance of labeled containers can be improved by shrinking plastic label material to fit tightly around the container and even follow the contours of a container to provide an enlarged billboard appearance.
Generally, labels are either spot-adhered to articles or are applied as pressure sensitive labels. Pressure sensitive labels generally are completely coated with an adhesive material and are one of the most expensive labeling options. Labels are also applied to containers by adhesive applied immediately prior to labeling. The adhesive may be applied in a variety of patterns including leading and trailing edge, spaced dots, picture frame, or overall adhesive.
In some applications, the minimum amount of adhesive is desired, particularly if a container is to be recycled. The prior art has failed to provide an inexpensive and effective labeling process that minimizes the use of adhesives, solvents, or complex welding mechanisms.
Other applications are better suited to a fully adhered label for an article or container. Generally, the more adhesive that is applied to a label, the greater the likelihood that the label will develop wrinkles or surface distortions. Distortions can also be caused by heat shrinking label material over the top of adhesive spots.
One application where a completely adhesive surface is desirable is where a label is to be applied over a previously printed can. Such a process would make it possible to use cans that have an outmoded decoration. By fully adhering a label to an overlabeled container, removal of the label can be substantially prevented or impeded.
Another situation where a fully adhesive label is desirable is in the labeling of containers that undergo a pasteurization process. For example, in breweries, bottles are pasteurized after filling by placing them in hot water or steam which can cause labels to peel off the containers or create bubbles and wrinkles under the label.
Another situation wherein fully adherent labels would provide an advantage is in the use of thin stretchable labels. For example, inexpensive polyethylene or polypropylene labels can be produced that offer many excellent characteristics for labeling but are elastic and can stretch. If a thin film label could be made to adhere directly to the article or container, problems relating to label stretch after application to the container could be eliminated.
One prior art approach to providing a fully adhesive label for cans was proposed in Canadian Patent No. 1,012,906 to Germiat. The Germiat patent proposed using a coextruded label material wherein a extruded layer of surlyn was provided to act as an adhesive. Both the label material and can to be labeled were heated in the Germiat method while the label was being applied to cause the label to become adhesive and fully adhere to the container. Disadvantages associated with the Germiat label were that the adhesive did not always activate uniformly which could lead to wrinkles or bubbles forming between the container and label, especially after pasteurization.
In another unique labeling application, heat is used to shrink labels over the contours of containers as is disclosed in U.S. Pat. No. 4,704,173 which issued to Hoffman. With shrink labeling, as proposed in the Hoffman patent, the leading and trailing edges of the label have hot melt adhesive applied thereto in a generally vertical line at the leading and trailing edges of the label. The balance of the label is preferably free of adhesive so that the label can shift as it shrinks without causing wrinkling of the label material. While the wrap shrink labeling process of the Hoffman patent is popular and effective for many labeling applications, the lack of a full coating of adhesive makes this approach inappropriate for some applications.
The above problems and limitations relating to the prior art are addressed by Applicant's invention as summarized below.